1. Field of the Invention
The present invention relates to a bearing apparatus, a spindle motor, and a disk drive apparatus.
2. Description of the Related Art
Hard disk apparatuses and optical disk apparatuses are typically provided with a spindle motor arranged to rotate a disk or disks about a central axis thereof. The spindle motor includes a stationary portion fixed to a housing of the apparatus, and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to produce a torque centered on the central axis by magnetic flux generated between the stationary and rotating portions, whereby the rotating portion is caused to rotate with respect to the stationary portion.
The stationary and rotating portions of the spindle motor are joined to each other through a bearing apparatus. In recent years, in particular, spindle motors have often been provided with a bearing apparatus in which a lubricating fluid is arranged between the stationary and rotating portions. JP-A 2002-5171, for example, describes an example of such a bearing apparatus using the lubricating fluid. In the bearing apparatus described in JP-A 2002-5171, the lubricating fluid is arranged to fill a gap between a shaft and a sleeve which are rotatably supported with respect to each other.
However, such a bearing apparatus using the lubricating fluid will deteriorate in rotational performance if air bubbles enter into the lubricating fluid so that the air bubbles are accumulated in the gap between the shaft and the sleeve. In the case where grooves are defined in the shaft or the sleeve to generate a dynamic pressure, in particular, air bubbles may become accumulated in the vicinity of the grooves so as to make it difficult for the dynamic pressure to be successfully generated in the lubricating fluid. This makes it difficult to achieve a sufficient supporting force between the shaft and the sleeve.